Lecture Notes (Week 1 and Weeh 2)

What is a Computer?

A computer is a programmable machine. The two principal characteristics of a computer are: it responds to a specific set of instructions in a well-defined manner and it can execute a prerecorded list of instructions (a program).

Computer is an advanced electronic device that takes raw data as input from the user and processes these data under the control of set of instructions (called program) and gives the result (output) and saves output for the future use. It can process both numerical and non-numerical (arithmetic and logical) calculations. The basic components of a modern digital computer are: Input Device, Output Device, and Central Processor. A Typical modern computer uses LSI Chips.

Computer Classification, By Size and Power

Computers can be generally classified by size and power as follows, though there is considerable overlap:

Ø  Personal Computer: a small, single-user computer based on a microprocessor. In addition to the microprocessor, a personal computer has a keyboard for entering data, a monitor for displaying information, and a storage device for saving data.

 

Ø  Workstation: a powerful, single-user computer. A workstation is like a personal computer, but it has a more powerful microprocessor and a higher-quality monitor.

 

 

Ø  Minicomputer: a multi-user computer capable of supporting from 10 to hundreds of users simultaneously.

 

Ø  Mainframe: a powerful multi-user computer capable of supporting many hundreds or thousands of users simultaneously.

 

 

Ø  Supercomputer: an extremely fast computer that can perform hundreds of millions of instructions per second.

 

Computer Hardware Definition

Hardware is a comprehensive term for all of the physical parts of a computer, as distinguished from the data it contains or operates on, and the software that provides instructions for the hardware to accomplish tasks. The boundary between hardware and software is slightly blurry - firmware is software that is "built-in" to the hardware, but such firmware is usually the province of computer programmers and computer engineers in any case and not an issue that computer users need to concern themselves with.

A typical computer (Personal Computer, PC) contains in a desktop or tower case the following parts:

• Motherboard which holds the CPU, main memory and other parts, and has slots for expansion cards
• power supply - a case that holds a transformer, voltage control and fan
• storage controllers, of IDE, SCSI or other type, that control hard disk , floppy disk, CD-ROM and other drives; the controllers sit directly on the motherboard (on-board) or on expansion cards
• graphics controller that produces the output for the monitor
• the hard disk, floppy disk and other drives for mass storage
• interface controllers (parallel, serial, USB, Firewire) to connect the computer to external peripheral devices such as printers or scanners

Computer Software Definition

Software is a generic term for organized collections of computer data and instructions, often broken into two major categories: system software that provides the basic non-task-specific functions of the computer, and application software which is used by users to accomplish specific tasks.

System software is responsible for controlling, integrating, and managing the individual hardware components of a computer system so that other software and the users of the system see it as a functional unit without having to be concerned with the low-level details such as transferring data from memory to disk, or rendering text onto a display. Generally, system software consists of an operating system and some fundamental utilities such as disk formatters, file managers, display managers, text editors, user authentication (login) and management tools, and networking and device control software.

Application software, on the other hand, is used to accomplish specific tasks other than just running the computer system. Application software may consist of a single program, such as an image viewer; a small collection of programs (often called a software package) that work closely together to accomplish a task, such as a spreadsheet or text processing system; a larger collection (often called a software suite) of related but independent programs and packages that have a common user interface or shared data format, such as Microsoft Office, which consists of closely integrated word processor, spreadsheet, database, etc.; or a software system, such as a database management system, which is a collection of fundamental programs that may provide some service to a variety of other independent applications.

Software is created with programming languages and related utilities, which may come in several of the above forms: single programs like script interpreters, packages containing a compiler, linker, and other tools; and large suites (often called Integrated Development Environments) that include editors, debuggers, and other tools for multiple languages.

The Internet

Internet is defined as a “connection of inter-connected networks all freely exchanging information”. Another definition viewed internet as “all the interconnected data sources and computers around the world”. Thus, it is a world-wide broadcasting capability, a mechanism for information dissemination and a medium for collaboration and interaction between individuals and their computers without regards to geographic location. Just as road networks link cities, and telephone networks link subscribers, the internet as a network of computers links the computers for the purpose of communication. The internet in this sense is a global infrastructure which enables any computer connected to it to communicate with any other computer connected to the internet at electronic speed, regardless of geographical location.

The Internet system comprises worldwide computer networks that communicate directly through internet protocol (IP), a computer language that allows any computer on any network to send data electronically to any other computer on an equal basis.  The real national highway system and the new information highway have similar military origin.  During the 1950s, American military and political leaders originally planned an inter-state highway grid to make it easier to transport military vehicles across the country in the event of a national emergency. The internet first started in 1960s as a defence communication system. It was initially called ARPAnet which means Advanced Research Project, but later known as the “net”, allowed military and academic researchers to conduct sensitive government probes that would survive even in the event of nuclear disaster. 

In developing the prototype for the military, Rand Corporation, a cold war think-tank conceptualized communications networks with no central authority. Each computer hub in the internet has similar status and power so nobody can own the system outright and nobody has the power to kick other off the network. There isn’t a master power switch, so authorities cannot shut off the internet in an emergency.

At its inception stage, the internet was strictly for military uses, where personnel from different locations interact with each other via interconnected computers. During the development stage of internet (1970s), the military computer network permitted different people in separate locations to communicate with one another by simply leasing existing telephone lines, they used the system to send letters and memos electronically (email) and to post information on computer bulletin boards, which are sites that list information about particular topics, such as health issues, computer programs and employment services. At this stage, universities and government research laboratories mainly used the internet: and later by corporations, especially companies involved in computer software and other high-tech products, to transmit and receive information.

By 1982, the Net had hit its entrepreneurial stage. The National Science Foundations invested in a high-speed communication networks designed to link computer centers around USA. This innovation permitted dramatically increased use of the internet. After the end of cold war in late 1980s, the ARPAnet project officially ended; by this time however a growing network of researchers, computer programmers, commercial interests and amateur hackers had tapped into the Net, creating tens of thousands of decentralized intersections. By 1993, the net developed multi-media capability allowing users to travel with pictures, sound and video.

The internet today consists of more than fifty thousand regional computer networks called servers, which are hosts run by universities, corporations and government agencies, all interconnected by special high speed phone lines.

 

The Internet in Africa

The Internet in Africa is limited by a lower penetration rate when compared to the rest of the world. Measurable parameters such as the number of ISP (Internet Service Provider) subscriptions, overall number of hosts, IXP (Internet Exchange Protocol) -traffic, and overall available bandwidth all indicate that Africa is way behind the "digital divide". Moreover, Africa itself exhibits an inner digital divide, with most Internet activity and infrastructure concentrated in South Africa, Morocco, Egypt as well as smaller economies like Mauritius and Seychelles.

Obstacles to the accessibility of Internet services in Africa include generally low levels of computer literacy in the population, poor infrastructures, and high costs of Internet services. Power availability is also scarce, with vast rural areas that are not connected to power grids as well as frequent black-outs in major urban areas such as Dar es Salaam.

In 2000, Subsaharan Africa as a whole had less fixed telephone lines than Manhattan, and in 2006 Africa contributed to only 2% of the world's overall telephone lines in the world. As a consequence of this general lack of connectivity, most Africa-generated network traffic (something between 70% and 85%) is routed through servers that are located elsewhere (mainly Europe).

 

Internet access

According to 2011 estimates, about 13.5% of African population has Internet access. While Africa accounts for 15.0% of the world's population, only 6.2% of the World's Internet subscribers are Africans. Africans who have access to broadband connections are estimated to be in percentage of 1% or lower. In September 2007, African broadband subscribers were 1,097,200, with a major part of these subscriptions from large companies or institutions.

Internet access is also irregularly distributed, with 2/3 of overall online activity in Africa being generated in South Africa (which, on the other hand, only accounts for 5% of the continent's population). Most of the remaining 1/3 is in Morocco and Egypt. The largest percentage of Internet subscribers are found in small economies such as Seychelles, where as much as 37% of the population has Internet access (while in South Africa this value is 11% and in Egypt it is 8%).

It has been noted, anyway, that data on Internet subscribers only partially reflect the actual number of Internet users in Africa, and the impact of the network on African daily life and culture. For example, cybercafes and Internet kiosks are common in the urban areas of many African countries. There are also other informal means to "access" the Internet; for example, couriers that print e-mail message and deliver them by hand to recipients in remote locations, or radio stations that broadcast information taken from the Internet.

Web Browsers

A web browser or Internet browser is a software application for retrieving, presenting, and traversing information resources on the World Wide Web. An information resource is identified by a Uniform Resource Identifier (URI) and may be a web page, image, video, or other piece of content. Hyperlinks present in resources enable users to easily navigate their browsers to related resources.

Although browsers are primarily intended to access the World Wide Web, they can also be used to access information provided by Web servers in private networks or files in file systems. Some browsers can also be used to save information resources to file systems.

 

History of Web Browsers.

The history of the Web browser dates back in to the late 1980s, when a variety of technologies laid the foundation for the first Web browser, WorldWideWeb, by Tim Berners-Lee in 1991. That browser brought together a variety of existing and new software and hardware technologies.

The introduction of the NCSA Mosaic Web browser in 1993 – one of the first graphical Web browsers – led to an explosion in Web use. Marc Andreessen, the leader of the Mosaic team at NCSA, soon started his own company, named Netscape, and released the Mosaic-influenced Netscape Navigator in 1994, which quickly became the world's most popular browser, accounting for 90% of all Web use at its peak (see usage share of web browsers).

Microsoft responded with its browser Internet Explorer in 1995 (also heavily influenced by Mosaic), initiating the industry's first browser war. By bundling Internet Explorer with Windows, Microsoft was able to leverage its dominance in the operating system market to take over the Web browser market; Internet Explorer usage share peaked at over 95% by 2002. Internet Explorer has 60% browser usage share as of September 2010 according to Net Applications, and it continues to show a negative trend.

Opera first appeared in 1996; although it has never achieved widespread use, with a browser usage share that is stable around 2.4% as of September 2010,[4] it has a substantial share of the fast-growing mobile phone Web browser market, being preinstalled on over 40 million phones. It is also available on several other embedded systems, including Nintendo's Wii video game console.

In 1998, Netscape launched what was to become the Mozilla Foundation in an attempt to produce a competitive browser using the open source software model. That browser would eventually evolve into Firefox, which developed a respectable following while still in the beta stage of development; shortly after the release of Firefox 1.0 in late 2004, Firefox (all versions) accounted for 7.4% of browser use.[3] As of September 2010, Firefox has a 23% usage share.

Apple's Safari had its first beta release in January 2003; it has a dominant share of Apple-based Web browsing, accounting for 5.3% of the entire browser market as of September 2010 and is slowly gaining.[4] Its rendering engine, called WebKit, is also running in the standard browsers of several mobile phone platforms, including Apple iOS, Google Android, Nokia S60 and Palm webOS.

The most recent major entrant to the browser market is Google's WebKit-based Chrome, first released in September 2008. Its market share has quickly risen; as of September 2010, it has an 8% usage share and appears to be gaining further in the coming months.

 Function

The primary purpose of a web browser is to bring information resources to the user. This process begins when the user inputs a Uniform Resource Identifier (URI), for example http://en.wikipedia.org/, into the browser. The prefix of the URI determines how the URI will be interpreted. The most commonly used kind of URI starts with http: and identifies a resource to be retrieved over the Hypertext Transfer Protocol (HTTP). Many browsers also support a variety of other prefixes, such as https: for HTTPS, ftp: for the File Transfer Protocol, and file: for local files. Prefixes that the web browser cannot directly handle are often handed off to another application entirely. For example, mailto: URIs are usually passed to the user's default e-mail application and news: URIs are passed to the user's default newsgroup reader.

In the case of http, https, file, and others, once the resource has been retrieved the web browser will display it. HTML is passed to the browser's layout engine to be transformed from markup to an interactive document. Aside from HTML, web browsers can generally display any kind of content that can be part of a web page. Most browsers can display images, audio, video, and XML files, and often have plug-ins to support Flash applications and Java applets. Upon encountering a file of an unsupported type or a file that is set up to be downloaded rather than displayed, the browser prompts the user to save the file to disk.

Interactivity in a web page can also be supplied by JavaScript, which usually does not require a plugin. JavaScript can be used along with other technologies to allow "live" interaction with the web page's server via AJAX.

Information resources may contain hyperlinks to other information resources. Each link contains the URI of a resource to go to. When a link is clicked, the browser navigates to the resource indicated by the link's target URI, and the process of bringing content to the user begins again.

Features

Available web browsers range in features from minimal, text-based user interfaces with bare-bones support for HTML to rich user interfaces supporting a wide variety of file formats and protocols. Browsers which include additional components to support e-mail, Usenet news, and Internet Relay Chat (IRC), are sometimes referred to as "Internet suites" rather than merely "web browsers".

All major web browsers allow the user to open multiple information resources at the same time, either in different browser windows or in different tabs of the same window. Major browsers also include pop-up blockers to prevent unwanted windows from "popping up" without the user's consent.

Most web browsers can display a list of web pages that the user has bookmarked so that the user can quickly return to them. Bookmarks are also called "Favorites" in Internet Explorer. In addition, all major web browsers have some form of built-in web feed aggregator. In Mozilla Firefox, web feeds are formatted as "live bookmarks" and behave like a folder of bookmarks corresponding to recent entries in the feed. In Opera, a more traditional feed reader is included which stores and displays the contents of the feed.

Furthermore, most browsers can be extended via plug-ins, downloadable components that provide additional features.